Surfaces of the Complete Denture

• Impression Surface• Occlusal Surface• Polished Surface– Facial surface (both maxillary and mandibular

denture)– Palatal surface (maxillary denture)– Lingual surface (mandibular denture)

Surfaces of a Complete Denture• Impression surface (Intaglio surface) • It is defined as, “That portion of the denture

surface which has its contour determined by the impression”

This surface refers to the surface of the denture that will be in contact with the tissues (basal seat area and limiting structures) when the denture is seated in the mouth. This surface is a negative replica of the tissue surface of the patient. It should be free of voids and nodules to avoid injury to tissues.

• Polished surface (Cameo surface)• It is defined as, “That portion of a surface of a denture

which extends in an occlusal direction from the border of the denture and includes the palatal surface. It is the part of the denture base which is usually polished, and it includes the buccal and lingual surfaces of the teeth”.

This surface refers to the external surfaces of the lingual, buccal, labial flanges and the external palatal surface of the denture. This surface should be polished and smooth to avoid collection of food debris.

• Occlusal surface• It is defined as, “That portion of the surface of

the denture teeth. It resembles the natural teeth and usually contains cusps and sluice ways to aid in mastication.

Occlusal: articulating surfaces of the prosthetic teeth that make contact during functuinal and parafunctional movements.

RECORD BASES

RECORD BASES

• AKA- Transfer base, trial denture base, temporary denture base.

• A material or device representing the base of a denture.

• It is used for making maxillomandibular relation records and arranging teeth

RECORD BASES

• USES- The primary function of the record base is to serve as a base to fabricate and support the wax occlusion rims and trial denture.

DIAGNOSTIC FUNCTION

• To determine the accuracy of the impression procedure. By checking the retention, stability and border extension of the record base the dentist gets an idea of the properties of the final denture .

• To see if a gag reflex is preset.• To observe if salivary flow is adequate or

inadequate.

REQUIREMENTS

A record base should be1. Well adapted to the final cast2. Stable and retentive in the mouth3. Rigid and dimensionally stable4. Smooth and not irritate the oral tissues5. No more than 1mm thick on the crest and facial slope of the

ridge (excess thickness may interfere with the placement of artificial teeth)

6. 2mm thick in the palatal and lingual flange region for rigidity7. Borders should be smooth and rounded and should produce

the reflection of the final cast.

MATERIALS USED AND CLASSIFICATION

1. Temporary bases2. Permanent bases

TEMPORARY BASES

• They are called temporary bases because they are discarded once their role in establishing jaw relation, teeth arrangement and try in is complete.

• They are discarded after waxing procedure.

The temporary record base materials are:

1. Shellac2. Autopolymerizing acrylic resin3. Vacuum formed vinyl or polystyrene4. Baseplate wax

Permanent bases

• The permanent bases are not discarded, instead they are incorporated as part of the finished denture.

• The materials used are1. Heat cured acrylic resin2. Gold alloy3. Chrome cobalt alloy4. Chrome nickel alloy5. Swaged metal base

SHELLAC

• It is thermoplastic material that was once very popular as a record base material. However, it can incorporate errors in the denture if it is not used carefully. It is available as preshaped, flat sheets in boxes.

Adaptation• The material is softened with a Bunsen flame

until it slumps. • It is adapted using moistened fingers or wet

cotton. • Adaptation is started from one palate

proceeding outwards to the ridge crest and onto the reflections.

• While it is still soft, it is removed and the excess trimmed with a scissor.

• The shellac is the repositioned and readapted. • The trimmed edges are then reheated with an

alcohol torch or Hanau torch, folded into itself, and burnished with a number 7 wax spatula

SHELLAC

• Precautions- Over heating is avoided as it can cause the material to stick to the cast, resulting in breakage of the cast surface during removal. Overheating can also cause bubbling, smoking and blackening, making it aesthetically unacceptable.

Undercuts in the cast are blocked out with wet asbestos (wax block out material can distort while heating the shellac). The cast is dusted with talcum powder or soaked in water to prevent the shellac from sticking to the cast. A well-adapted tinfoil (0.001 inch) may also be used.

SHELLAC

Advantages1. It is inexpensive and easily available2. It is easy to use and adaptDisadvantages3. It is a brittle material and can break easily during clinical use.4. Being thermoplastic, it tends to warp or distort when heated

repeatedly.5. Recording jaw relations becomes difficult, if distorted and

unstable.6. An unstable or loose denture base is demoralizing the patient.

AUTOPOLYMERIZING RESIN

• Autopolymerizing resin record bases have the advantage of strength, better stability to heat and dimensional stability which improves the accuracy of jaw relation records.

Adaptation

• There are three basic techniques– Nonflasking method– Alternate application of monomer and powder– Flasking method

Nonflasking or adapting method

• For all three techniques undercuts are blocked out with wax and tinfoil substitute (sodium alginate separating media) is applied.

• Self curing resin is mixed and when it reaches the dough stage it is rolled to a cigar shaped, places on a roller board and rolled to the desired thickness (2 to 3 mm).

The roller and fingers are lubricated with petrolatum to prevent the resin from sticking. The resin sheet is adapted starting from the palate. The excess is trimmed with a sharp instrument. After it has hardened, the record base is smoothened and polished.

• Polymer and monomer are applied alternatively to get the desired thickness of the record base. The polymerization shrinkage is minimized. Any undercut on the fitting surface is blocked

out with wax or clay.

Flasking method

• The master cast is duplicated and a wax pattern is formed.

• The pattern is then flasked and duplicated in auto polymerizing resin.

• The resin is allowed to cure for 20 to 30 minutes, then flasked and finished.

• Advantage: More accurate and stable• Disadvantages: 1. More time consuming

2. Higher cost

VACUUM FORMED BASES

• Using a sheet of thermoplastic resin and a thermal vacuum machine, the record base is formed. Depending on the material

BASEPLATE WAXBaseplate wax is softened over a flame and adapted onto a moist cast or a cast dusted with talcum powder. A wire may be adapted for additional strength and rigidity.Advantages1. Inexpensive2. Easy to form3. Esthetic4. Easy to set teeth when

interridge space is less.Disadvantages - Lacks rigidity and dimensional stability

PERMANENT BASES

Heat Cured Resin• A wax pattern of the denture base is made on a duplicate cast and

processed with heat cured resin.

Advantages• Rigid accurate and dimensionally stable.• Retention and stability can be tested in the mouth much before

the denture is delivered.Disadvantages• The master cast gets damaged during processing so a duplicate

had to be constructed.• Time consuming and therefore more expensive.

Cast alloy denture bases• A metal base is usually made by casting gold

alloys or base metals alloys (e.g. chrome cobalt). Artificial teeth are set in wax on the denture base and replaced later with processed resin as in the regular technique.

AdvantagesThey add more weight to the mandibular dentures.Good thermal conductivity and so improved oral feeling and sensitivity.Because of their higher rigidity they can be made thinner or so less bulk in the palatal region.Can be given for patients who repeatedly break their dentures.

DisadvantagesMore time needed for pabrication.More expensive.

OCCLUSION RIMS

• Record rims bite rims, occlusal rim.• Occluding surfaces fabricated on interim or

final denture bases for the purpose of making relationship records and arranging teeth

USES

1. Determination of lip support and facial esthetics.2. Determination of arch form.3. Determination of the plane of occlusion.4. Aids in establishing teeth size and position.5. To establish the contour of the polished surface.6. For the (tentative) establishment, recording and

transfer of jaw relation.7. To see the patient’s response to a denture-like form.8. Arrangement of artificial teeth.

FABRICATION OF OCCLUSION RIMS

• A sheet of baseplate wax is softened over a Bunsen burner and rolled into a cylindrical shape taking care not to entrap air.

• The soft rolled is adapted on to a record base and formed to the approximate contour of the occlusion rim.

• The wax is sealed to the base with a hot spatula. • The axial surface is shaped with a heated plaster spatula or

broad bladed putty knife. • The heated surfaces are shaped with a heated wax spatula.• Readymade wax occlusion rim forms are available

commercially.• The completed occlusion rims are shown in.

OCCLUSION RIM SHAPE, DIMENSIONS AND POSITION

The edentulous arch form may be classified as• Square (“U” shaped)• Tapering (“V” shaped)• Ovoid

The occlusion rim form generally follows the form of the arch. Thus the occlusion rim can also have a square, tapering or ovoid form.

Position of the occlusion rims

• The occlusion rim usually occupies the position occupied by the natural teeth which is usually located within the neutral zone.

• Violation of the neutral zone by the occlusion rim can lead to instability or displacement.

• Posteriorly, the occlusion rim is entered over the crest of the ridge, whereas anteriorly, it is slightly labial to the crest.

Inclines of the lateral surfaces•Anteriorly, the surface inclines outward or labially. •Posteriorly, it inclines inwards towards the ridge crest.

Width- The width of the occlusion rim anteriorly is approximately 5 mm and posteriorly it is between 8 to 10mm

Maxillary Rim Height- Anteriorly, it has a height of 22 mm from the reflection of the cast. Posteriorly, it is adjusted to the height of the first molar (approximately 5 to 7 mm from the crest of the ridge or 18 mm from the bucal sulcus)

Mandibular Rim Height- The height of the occlusion rim is 16 mm anteriorly. In the posterior section it is adjusted to a height equaling one half of the retromolar pad (or two-thirds according to some authors).

CUSTOMIZING THE OCCLUSION RIMS AND ESTABLISHING MAXILLOMANDIBULAR RELATIONS

• The shape and dimensions of the occlusion rims constructed in the laboratory are only tentative. The wax occlusion rims represents the dental arch. During the clinical phase, the occlusion rims are tried in the patient’s mouth and reshaped. The dentist attempts to establish the form of the occlusion rims that is most suited for the patient.

This is done with the help of certain guidelines. Clinical experience is invaluable in this regard. The corrected occlusion rums are useful to the technician as it will serve as a template and guide for the arrangement of the artificial teeth.Although it is popularly known as a jaw relation appointment, there are many different procedures which take place during this appointment.

Procedures

1. Establishing the labial form of the occlusion rims.

2. Establishing the occlusal plane.3. Establishing vertical jaw relations.4. Establishing and recording of centric jaw

relations.5. Facebow transfer.6. Selection of artificial teeth.

Difficulties• This appointment is probably the most vexing of all appointments to

the novice. • This is because many of the procedures are based on operator

judgments which require keen observation and a fair amount of experience.

• There is no single fixed rule for determining any of the maxillomandibular relations and occlusion rim contour and often a combination of technique is required.

• Facial esthetics and teeth positions vary between patients.• Another problem is that of patient cooperation especially during

centric relations. • Many patients find it difficult to follow the dentist’s instructions leading

to frustration on the part of both the patient and the dentist.

TRY-IN OF THE OCCLUSION RIMS

Record base interferences- The record bases are also checked intraorally for interferences while closing or during the lateral movements. Occasionally, interferences may be seen in the posterior portion between the upper and lower record bases. These are trimmed when present, as they can cause errors during jaw relations. It can also cause pain and injury as the tissues get pinched between the upper and lower rims in the region.

• Stabilized denture bases- The occlusion rims are tried in the

patient’s mouth and checked for retention and stability. Jaw relations are difficult to record if the record bases are unstable. The records may also be questionable. Acrylic record bases are relatively unstable. In case of unstable record bases, the stability and retention can be improved by lining it with a thin layer of a suitable material (zinc oxide eugenol or elastomeric impression material). This is known as a stabilized record base. Tin foil is adapted to the cast before placing the lining material. The rubber is a very effective stabilization material if severe undercuts are present.

ESTABLISHING THE LABIAL FORM OF THE OCCLUSION RIM

• Aim: This procedure establishes the anteroposterior position of the anterior teeth and the esthetics of the lips and face.

• As mentioned before the occlusion rim represents the dental arch and therefore establishing the size and form of the occlusion rims will guide us in determining the size and position of the artificial teeth. Assuming that the patient has no previous records of tooth size and position, the dentist has to use clinical guidelines to establish the occlusion rim shape, height and inclination.

• The question is how far forward should the wax rim extend? This determines the anteroposterior position of the artificial teeth. Anterior teeth are usually inclined labially, and therefore the occlusion rim should also have a labial inclination. When no previous preextraction records are present, the form and inclination of the anterior part of the occlusion rims is established based on the clinical experience and judgment of the operator. The operator uses the following as guides

• Facial esthetics as guides• Phonetic guidelines

Facial estethics as guide• The esthetics of the face is a reliable guide to the anterior

form of the upper occlusion rim.• The following facial landmarks are used as guide.1. Fullness of the upper lip2. The philtrum3. The nasolabial fold4. Commissures of the mouth• When the wax rims assume the right form the above

landmarks will assume a normal end and pleasing appearance. The dentist should be able t recognize the optimal appearance for the patient.

Fullness of the lips

• Inadequate support- makes the upper lip look flabby and unsupported. There is a deepening of the nasolabial creases or folds. (Other creases on the face will also appear to darken or deepen). A loss of definition of the philtrum may be noticed. There is also a drooping or lowering of the commissures of the mouth. In this case modeling wax is added and blended to the labial surface. This process is continued until the lip is well supported and the face assumes normal appearance.

Exessive fullness

• results in the ‘stretched look.’ The philtrum appears shallow and the nasolabial fold appears smooth. The corners of the mouth appear stretched outward. In case of excessive fullness, the wax is removed from the labial surface of the occlusion rim, until the features assume normal appearance.

The nasolabial fold

• The nasolabial folds like the philtrum can serve as a useful guide to the anteroposterior position of the occlusion rims. The nasolabial folds can look filled out or almost invisible when the occlusion rims are too far forward. The labial surface of the occlusion rims are reduced until the nasolabial fold assumes its normal appearance.

The philtrum

• The philtrum of the lip is a useful guide. One should learn to recognize the normal appearance of the philtrum by observing dentate individuals. The philturm can look filled out and flattened when the labial surface of the occlusion rim is too far forward or if the labial borders are too thick. Reducing the thickness of the border or removing wax from the labial portion of the occlusion rims can restore normal appearance of the philtrum. Occasionally, one does see patients where the anterior ridge is procumbent. This can create some confusion in judgment.

Other facial lines and creases

• The geriatric patient may have a considerable amount of facial lines and creases. These may get exaggerated when the teeth are lost. Occasionally patients may ask for their elimination by plumbing out the occlusion rims. One should be careful as many of these facial creases are a natural result of advancing years and trying to eliminate them by increasing the fullness of the occlusion rims can be disastrous.

• Commissures of the mouth• The corners of the mouth may also be used as a guide to the shape

of the occlusion rims and the vertical height.• The buccal corridor• The “buccal corridor” is a term used to describe the space between

the buccal surface of the posterior teeth and the inner surface of the cheeks. The buccolingual positioning of the occlusion rim should permit an appropriate buccal corridor. An extensive buccal corridor or space results when the posterior parts of the occlusion rims are positioned too far lingually. The resulting dark space is may appear excessive and unesthetic. An inadequate buccal corridor occurs when the posterior teeth are too bucally positioned resulting in the obliteration of the buccal corridor.

ESTABLISHING LEVEL AND INCLINATION OF THE OCCLUSAL PLANE

• Aim - This phase establishes the superoinferior position of the teeth especially that of the anterior teeth. The level and slant of the plane of occlusion is also determined. The occlusal plane is the plane at which the upper and lower teeth meet during occlusion. Thus, establishing the occlusal plane also aids in establishing the superoinferior position of the teeth in relation to the basal bone. When teeth are lost (especially the posterior teeth) the occlusal plane has to be reestablished. This is done with the help of certain guides.

• There are two ways of establishing the occlusal plane.

Method 1 – Establishing occlusal plane using the maxillary occlusion rim.

Method 2 – Establishing the occlusal plane using the mandibular rim.

Establishing occlusal plane using the maxillary occlusion rim.

• Establishing the anterior height of the rims• Incisal visibility- Establishing the height of the anterior portion of the

occlusion rims establishes the superoinferior position of the anterior teeth. The incisal visibility and length of the upper lip is used as a guide (provided it is of normal length). This is a common method and relatively simple. In most individuals, the upper incisors are visible by 1 to 2 mm when the lips are at rest and the mouthis slightly open (fig 9-1). This is known as incisal visibility. The incisal visibility varies between individuals because of differences in anterior jaw height, lip length and lip tonicity. As age advances the incisal visibility reduces because of incisal wear. A mark is made on the occlusion rims about 1 mm below the level of the upper lip at rest (low lip line). The anterior portion of the occlusion rim is reduced to his level using a heated broad spatula or putty knife.

• Interpupillary line- The anterior portion of the occlusion plane should parallel a line passing through the pupils of the eye (interpupillary lin – fig 9-3).

• Drawbacks- The problem with this technique is the variation in lip length and tonicity between different individuals and is therefore not a highly reliable guide. Overall facial esthetics have to be re-assessed at the try-in stage.

Establishing the posterior height of the occlusion rims

• After reducing the anterior part of the occlusion rim to this level the posterior part is then adjusted to make it parallel to the ala-tragus line. This is generally done with the help of Fox plane guide – fig. 9-5 A and B (also known as occlusal plane indicator or guide). Thus, when viewed from the side, it should be parallel to the ala-tragus line. A technique involving two plastic rules may also be used (fig. 9-4 A and B). posteriorly, some dentists are the Stensen’s duct as a guide – the occlusion plane is leveled at about quarter inch below the Stensen’s duct.

Establishing the occlusal plane of the lower occlusion rim

• Once the occlusal height of one of the occlusion rims is established, the vertical height of the opposing rim is easily determined. The lower occlusion rim height is adjusted to provide for an interocclusal rest space of 2 to 4 mm the it meets the upper occlusion rim evenly (figure. 9-6).

Establishing the occlusal plane using the mandibular occlusion rim

• The occlusal plane may be determined using the lower occlusion rim. Some dentists prefer to start with the lower occlusion rim.

• Anterior height- The anterior part is adjusted to the level of the corner of the mouth. No more than 0.5 mm of the anterior portion of the lower occlusion rim should be visible when the jaws are at rest and the lip is slightly parted.

• Posterior height -The posterior height is adjusted so that it is at level of the middle of the retromolar pad or the junction between the upper one-thirds.

• Establishing upper occlusion rim plane Once the lower occlusal plane is established, the upper occlusion rim is adjusted so the there is an interocclusal rest space of 2 to 4 mm. There are various methods to achieve this (discussed under vertical jaw relations). The upper occlusion rim is then leveled such that it meets the lower occlusion rim entirely.

• Bilateral Symmetry• The cheeks on both sides are retracted and

the operator checks for bilateral symmetry with regard to the level and slant of the occlusal plane.